XB-ART-41492Dev Biol. August 6, 2010; 1347 19-32.
Sonic hedgehog expression during Xenopus laevis forebrain development.
We have analyzed the developing expression pattern of x-Shh in the Xenopus forebrain, interpreting the results within the framework of the neuromeric model to assess evolutionary trends and clues. To achieve this goal, we have characterized phenotypically the developing x-Shh expressing forebrain subdivisions and neurons by means of the combination of in situ hybridization for x-Shh and immunohistochemistry for the detection of forebrain essential regulators and markers, such as the homeodomain transcription factors Islet 1, Orthopedia, NKX2.1 and NKX2.2 and tyrosine hydroxylase. Substantial evidence was found for x-Shh expression in the telencephalic commissural preoptic area and this is strongly correlated with the presence of a pallidum and/or a basal telencephalic cholinergic system. In the diencephalon, x-Shh was demonstrated in the zona limitans intrathalamica and the x-Shh expressing cells were extended into the prethalamus. Throughout development and in the adult hypothalamic x-Shh expression was strong in basal regions but, in addition, in the alar suprachiasmatic region. The findings obtained in the forebrain of Xenopus revealed a largely conserved pattern of Shh expression among tetrapods. However, interesting differences were also noted that could be related to evolutive changes in forebrain organization.
PubMed ID: 20540934
Article link: Dev Biol.
Genes referenced: hopx isl1 nkx2-1 nkx2-2 otp shh th
Article Images: [+] show captions
|Fig. 1. Photomicrographs of in toto views illustrating the x-Shh expression in early embryonic stages (from st 13 to st 35–36). Scale bars= 500µm (a,b) and 100µm (c-h).|
|Fig. 5. Photomicrographs of doubly labeled transverse sections through the Xenopus developing forebrain showing the x-Shh expression at premetamorphic stages in combination with NKX2.1 (a, e, f, g, j), TH (b–d, k–m) and ISLET1 (n). At preoptic regions, the double x-Shh/NKX2.1 labeling confirmed the x-Shh telencephalic expression in the preoptic commissural area (a), whereas the double x-Shh/TH staining delineates the preoptic area (b, c). Similarly, x-Shh/TH (d) and x-Shh/NKX2.1 (g) allowed the identification of the SC, rich in TH and NKX2.1 expressing cells (see arrowhead in g). In the diencephalon, the x-Shh expressing cells in the Zli extend into the prethalamic (P3) territory, showing NKX2.1 expression (arrowheads in e and f). In posterior diencephalic levels, the x-Shh detected was situated in P3 by the double x-Shh/NKX2.1 (h–j), and specifically in the zona incerta, according to the TH expressing cells detected (k). The double labeling for x-Shh/TH (l, m) and x-Shh/ISLET1 (n) allowed the identification of the mammillary and tuberal boundaries. Scale bars = 100 μm (a–n) and 50 μm (b′).|
|Fig. 6. Photomicrographs of transverse (a–e) and horizontal (f) sections through the Xenopus developing forebrain showing x-Shh expression in combination to OTP (a–c) and NKX2.2 (d–f). The exclusive expressions of x-Shh, rich in preoptic and preoptic commissural areas, with OTP, rich in the supraoptoparaventricular area, allowed the identification of the boundary (a–c; see asterisk in c). The combination with NKX2.2 confirms the x-Shh expression in the zona limitans intrathalamica (d, e), and the x-Shh and NKX2.2 expression in the suprachiasmatic area (d, f). Scale bars = 100 μm.|